Article Pistol Caliber Carbines

For years I have had a 45ACP DI (gas operated) AR-15 which runs great and is very accurate, but as of late I wanted to add a couple of uppers in 9mm and 45GAP so I contacted Ron Williams of RMW XTREME in Florida to build the uppers. Ron was also the one that built my 45ACP upper so I knew he was the person to go to. I did not want to go with a blowback upper because of the need to run a very heavy buffer and recoil spring, in speaking with Ron he builds all of his pistol caliber DI uppers to run with standard carriers (semi auto and full auto depending on if you have a registered lower with the happy switch) and standard buffers for factory ammo and if you want to run powder puff or barn burners you can change the buffer to a no weight with a lite weight spring or H1,H2 with a standard spring or a heavy spring if needed. I ordered an NFA (New Frontier Armory) Glock pistol lower that takes Glock 9mm mags, the lower is setup for blowback so I had to remove the blowback ejector to use it with the DI uppers. I went thru the ATF process to SBR the lower and once I received the stamp back, I had Ron build the uppers. Both are 10.5” barrels threaded for a suppressor as well, I also went with 15” Sampson handguards so most of the suppressor is inside of the handguard. A word of caution if you have a similar setup be very careful if you shoot it without the suppressor and know where your hand placement is so you do not get burned or injured from the muzzle blast. There are some things that need to be said about pistol caliber DI AR uppers and especially for the 9mm. With the gas systems being so short in order to cycle the action the actual placement and diameter of the gas port are critical to get them to run correctly. One of the other issues is that with the gas system so short they tend to run dirty and with the 9mm more so than other calibers. With that being said I would not recommend the DI 9mm upper unless you reload and can use cleaner powders and optimize loads for the gun. In speaking to Ron he has several people with DI 9mm uppers that are using them in competition and tailored their loads for the gun and run 500-1000 + rounds before needing to clean and lube the uppers. One of the things I did for both the 9mm and 45GAP was to get complete bolt carriers that were coated with nickel Teflon and nickel boron to make them easier to clean then standard carriers. Since the carriers are standard AR carriers Ron does open the bolts up for the cartridge and tweaks the extractor if needed to guarantee they work 100%. When I picked up the uppers I was able to run a mag of 165gr handloads in the 9mm and some 280gr cast handloads in the 45GAP to do a quick function test, both ran great and cycled 100%.

Since I do not have sights on the uppers yet I did not try for any accuracy testing, I was just sighting down the handguards and very low on the mound as I did not want to have any stray shots. The first couple of rounds were slow fire then did a dump as fast as I could pull the trigger. By this time I had noticed something that was a pleasant surprise, the lack of recoil, the 9mm felt like I was shooting a 22 LR upper and the 45GAP had just a tad more recoil but I was amazed by the lack of recoil of both uppers. For the last couple of rounds I had left I put my 45 TiRant suppressor on both the 9mm and 45GAP to see how they both sounded suppressed and to see if any issues would arise from the suppressor. No issues came up and both guns ran 100% with the handloads I brought.

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A couple of weeks after picking up the uppers I had a chance to take the 9mm out and run some rounds down range. I plan to run both of these uppers suppressed most of the time and will work up some different loads and start to do accuracy testing. Here is the last few rounds I had left during this range trip so I shot a group @ about 30yds, the load is a 165gr XTREME plated bullet on a charge of longshot loaded to 1.164". To say this load has promise is an understatement. I will be loading more with longshot and testing for accuracy as I hope this group was not a fluke.

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Now granted this outing I had only 50 rounds loaded and was mainly function testing and I had one failure to feed which was caused by the cartridge overall length was a tad long for the after market mag, but I had no issues feeding from factory Glock mags (I will be reducing the powder charge and seating the bullet to a COL of 1.14" and should not have that problem anymore.).

After running 50 rounds thru the gun I pulled the bolt carrier and inspected it to see how much carbon build up there was. The tail of the bolt had some carbon build up but was cleaned easily. The carrier also had some crud on/in it and cleaned up easily as well. I went with a nickel boron coated bolt and carrier to make sure clean up easy and also to help prevent carbon buildup. I think that was a good choice as this first clean up was done with a dry paper towel. Here is the bcg before being cleaned.

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There are several mods that have to be done to the standard 223 carrier so it can go thru the magazine opening and strip a round, without doing this mod the carrier will hang on the mag. In the picture below you can see the carrier mod and also the slight opening of the 223 bolt for the 9mm rim.

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The feed angle on the New Frontier Armory lower is spot on. In the past other manufacturers Glock mag lowers positioned the mag to high or to low and tried to compensate by changing the angle of the magazine in the lower and caused feeding issues.

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Over the next few weeks I hope to get to the range and do some load development and velocity testing completed, and once I settle on a load I will load up 1500 or so and see how far it will go with out cleaning before it malfunctions. I think with some fine tuning of the loads this will be a great gun for competition and a general fun shooter. I also want to get a sight for the 45GAP upper and get started on load development and velocity testing as well and I will do updates on the progress of both uppers.

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Interesting DATA, Thank You for your time and PICS to help understanding ! I keep trying to get the caliber count lower and lower. Started out getting everything and anything just to know as much as I could and learn / learn / learn.
Ended up selling off many of the herd that I made poor buying decisions with, and it cost me dearly...
Now - its research and realization of what I can utilize and what others of my family and friends can utilize with minimal lessons of anything truly terrible should ever occur ! limit the calibers / choose the best for all around utilization and effective capabilities and also as to the conversion of long to short and back again, All legal of course ! Again, Thank You for the time and patience it took to make an informative article. PR

Nice work, I was wondering if anyone makes a Glock 45 ACP or 10mm mag compatible lower? That would really be a hard hitting PCC!
What are the advantages of using DI over blowback in a PCC?
Are the blowbacks a bit cleaner? I'd think the DI would gain some velocity since it has the locking bolt.
Your thoughts appreciated

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They both tend to be dirty, most commercial ammo burns dirty. If you reload you can taylor loads and run clean. I have noticed with say ww white box after a hundred rounds or so I have to clean the carrier and bolt. With handloads I have run 600+ with no issues. 10mm and 10mm mag are no problem, with the 10 mag you need to do some magazine mods or find a mag and block to make it work.

Nice work, I was wondering if anyone makes a Glock 45 ACP or 10mm mag compatible lower? That would really be a hard hitting PCC!
What are the advantages of using DI over blowback in a PCC?
Are the blowbacks a bit cleaner? I'd think the DI would gain some velocity since it has the locking bolt.
Your thoughts appreciated
There are many different pcc AR15 uppers, RMW XTREME does 9mm to 50AE. I have 45acp, 45WinMag and 10mm all are great and fun to shoot. The big pluses for going DI over blowback is in blowback you have to run heavy carrier, heavy buffer and sometimes heavy springs so they do not open early. For the DI, you use standard carrier, modified bolt and standard spring. In a blowback 45acp it is common to run a 10-13oz buffer and with that much weight recoil go up. I have shot both DI and blowback FA and the difference is remarkable.

Interesting. First of all, it should not make a difference if the bolt carrier is semi or full auto...only weight being an issue as both are legal in a semi auto gun. Sad that he had to settle with the Gap round....it has it's limitations. And loading a 9mm to 1.164 inches is REALLY stretching it! Also using 165 grain bullets? Go with the 147 grain bullets at 900fps. You can use smaller charges of powder and be subsonic and get better accuracy. I use that as a match load in many 9mms. I have a lot of match shooters that use this load.

There are several issues with a DI 9mm, smaller powder charges do not provide enough gas to run the system reliably. I currently do not have any 147gr bullets but I have several boxes of the 165gr bullets so that is what I used. Also running heavier bullets you can extend the dwell time and help the system run. I am doing load development and I am looking @ a COL of 1.15-1.16" @ that length I am able to run more powder.

Sorry, been busy and did not see your question. As for both questions I do not know, I do know the gas system is very short the gas block is very close to the barrel nut. As for the port diameter I do not know, Ron has spent several years perfecting the system. As far as I know he is the only one that has it working 100%. Others have tried and not successful in getting it going.

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